1. Field of the Invention
This invention relates to an organic EL (electro-luminescence) device that operates as an electric light emitting device for use in a display, a display light source, etc, and to a method of manufacturing thereof.
2. Description of Related Art
Recently, development has been accelerated of organic EL display devices using organic materials as spontaneous light emitting displays that will replace liquid crystal displays. Organic EL devices using the organic materials are principally described in the reference “Appl. Phys. Lett.” 51(12), 21 Sep. 1987, p913, that discloses a vacuum deposition method of organic materials having a low molecular weight, and in the reference “Appl. Phys. Lett.” 71(1), 7 Jul. 1997, p.34 et seq., that discloses an application method of organic materials having a high molecular weight.
In order to achieve color display in the case of the low molecular weight materials, a method that vacuum deposits different light emitting materials onto desired pixels through a mask has been employed. As to the high molecular weight materials, on the other hand, a coloring method using an ink jet method has drawn attention because it can execute patterning delicately and easily. Examples of the formation of organic EL devices by the ink jet method are disclosed in Japanese Patent Laid-Open Nos. 235378/1995, 12377/1998, 153967/1998, 40358/1999, 54270/1999 and 339957/1999.
A device structure includes a hole injection/transportation layer formed in many cases between an anode and a light emitting layer to enhance light emission efficiency and durability (“Appl. Phys. Lett.” 51, 21 Sep. 1987, p913). The term “hole injection/transportation layer” used herein is a generic term of a layer that has a function of injecting and transporting holes from the anode side to a light emitting layer. According to the related art technology, a film of a buffer layer or a hole injection/transportation layer is formed by using conductive polymers, such as polythiophene derivatives or polyaniline derivatives, by an application method, such as spin coating (“Nature”, 357, 477, 1992). The hole injection/transportation layer can be formed by vacuum depositing phenylamine derivatives as the low molecular weight material.
An ink jet system is extremely effective to easily form a film having a miniature pattern without wasting organic thin film materials.
However, when an organic EL device, having a laminate structure, is formed in accordance with the ink jet system and moreover, when the laminate structure includes a hole/injection layer plus a light emitting layer, for example, an underlying layer, as the conductive layer, is exposed when a cathode is formed, if an application region of the hole injection/transportation layer, as the underlying layer, is broader than the application region of the light emitting layer as an upper layer, with the result that a current leaks and the resulting device has low efficiency.